The "health halos" of healthy restaurants often prompt consumers to treat themselves to higher-calorie side dishes, drinks or desserts than when they eat at fast-food restaurants that make no health claims, according to a series of new Cornell studies.

The research, published in the October online version of the Journal of Consumer Research, found that many people also tend to underestimate by 35 percent just how many calories those so-called healthy restaurant foods contain.

"We found that when people go to restaurants claiming to be healthy, such as Subway, they choose additional side items containing up to 131 percent more calories than when they go to restaurants like McDonald's, that don't make this claim," says Brian Wansink, author of "Mindless Eating: Why We Eat More Than We Think" (Bantam 2006) and the John S. Dyson Professor of Marketing and of Applied Economics and director of the Cornell Food and Brand Lab.

Wansink and co-author Pierre Chandon, a marketing professor at INSEAD, an international business school in France, also report that by simply asking people to reconsider restaurants' health claims prompts them to better estimate calories and not to order as many side dishes.

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They recommend that public policy efforts help people to better estimate the number of calories in foods.

"In estimating a 1,000 calorie meal, I've found that people on average underestimate by 159 calories if the meal was bought at Subway than at McDonald's," says Wansink. Since it takes an energy imbalance of 3,500 calories to put on one pound, that extra 159 calories could lead to almost a 5-pound weight gain over a year for people eating at Subway twice a week compared with choosing a comparable meal at McDonald's with the same frequency, he says.

These studies, he says, help explain why lower-calorie menus at fast-food restaurants have not led to the expected reduction in total calorie intake and in obesity rates.